Method and apparatus for optical analysis of the contents of a sheathed stream

ABSTRACT

There is provided a method and apparatus for optical analysis by photometry of a substance flowing in a liquid stream within a coaxial sheath stream of a transparent liquid. The sheath stream, flowing in the same direction, entrains the inner stream so as to confine it concentrically. A photometer is used which includes a light source on one side of the sheathed stream in a position to direct light onto the inner stream which is cylindrical, the outer or sheath stream also being cylindrical. The photometer also includes a light detector externally of the sheathed stream in an angular position to detect the photometric results of impingement of light on the contents of the inner stream. Refraction of light at the interfaces of the sheath stream is compensated by varying the radius of the inner stream through the control of the flow of one stream with reference to the other. The concept also includes the narrowing of the sheathed stream to a very small diameter in which it is confined by a wall structure in the area of examination.

United States Patent [151 3,66 1,460 Elking et a1. May 9, 1972 54 METHODAND APPARATUS FOR 3,504,183 3/1970 Salkowski et al. ..356/103 x OPTICALANALYSIS OF THE 3,515,884 6/1970 lmadate ..250/218 3,523,733 8/1970Kling at al.... ...356/208 x CONTENTS OF A SHEATHED STREAM 3,560,7542/1971 Kamentsky ..356/39 x Inventors: Alan H. Elking, White Plains;Warren Groner, Whitestone; Alex M. Saunders, Bedford Village. all of NY.

[73] Assignee: Technicon Instruments Corporation, Tarrytown, NY.

[22] Filed: Aug. 28, 1970 [2]] Appl. No.: 67,819

[52] U.S. Cl. ..356/36, 250/218, 250/222 PC, 356/102, 356/208, 356/246[51] Int.Cl. ..G01n1/00,G01n15/02,G01n2l/06 [58] Field of Search..356/36, 39-40, 356/102-104, 134, 201, 207-208, 246; 250/218, 222 PC [56] References Cited UNITED STATES PATENTS 2,731,877 1/1956 Clamann..250/218 X 2,732,753 1/1956 OKonski ..356/103 X 2,875,666 3/1959 Parkeret al.. ..250/218 X 2,920,525 1/1960 Appel et al... 356/102 X 3,398,2868/1968 Ford et a1 ...356/103 X 3,440,866 4/1969 Ness et a1 ..356/39 X 14PUMP T0 OVERFLOW 3) Primary Examiner-Ronald L. Wibert AssistantE.raminer-Warren A. Sklar Attorney-S. P. Tedesco and Rockwell S. E.

[57] ABSTRACT There is provided a method and apparatus for opticalanalysis by photometry of a substance flowing in a liquid stream withina coaxial sheath stream of a transparent liquid. The sheath stream,flowing in the same direction, entrains the inner stream so as toconfine it concentrically. A photometer is used which includes a lightsource on one side of the sheathed stream in a position to direct lightonto the inner stream which is cylindrical, the outer or sheath streamalso being cylindrical. The photometer also includes a light detectorexternally of the sheathed stream in an angular position to detect thephotometric results of impingement of light on the contents of the innerstream. Refraction of light at the interfaces of the sheath stream iscompensated by varying the radius of the inner stream through thecontrol of the flow of one stream with reference to the other.

The concept also includes the narrowing of the sheathed stream to a verysmall diameter in which it is confined by a wall structure in the areaof examination.

19 Claims, 6 Drawing Figures 12 CONSTANT LEVEL RESERVOIR 40 SHEATHSOURCE 28 NEEDLE VALVE 0R RESISTOR LIGHT DETECTOR 26 VACUUM PUMPREGULATOR PATENTEUNNT 9 I972 3,661,460

SHEET 1 0T 3 FIG. 1

T4 PUMP To OVERFLOW\ P T 1 WWW LEVEL H RESERVOIR 28 i0 1 NEEDLE VALVE 0RSSOHUERACTEH RESISTOR LIGHT DETECTOR 2e I5 I f m ucNT l souRcE 25 QSwREGULATOR k E 2| LIQUID 22 TRAP INVENTORS ALAN H. ELKIND WARREN GRONERALEX M. SAUNDERS ATTORNEY METHOD AND APPARATUS FOR OPTICAL ANALYSIS OFTHE CONTENTS OF A SHEATI'IED STREAM BACKGROUND OF THE INVENTION 1. Fieldof the Invention This invention relates to a method and apparatus foroptical analysis by photometry of a substance flowing in a liquid streamwithin a coaxial sheath stream of a transparent confining liquid inwhich it is entrained.

2. Prior Art Fine streams utilized for optical examination of theircontent frequently clog in small diameter transparent tubing as is wellknown, especially in circumstances where the stream contains,intentionally or otherwise, particulate matter. Also, it has long beenrecognized that in the use of such fine tubing there is an undesirablepressure drop. I

At least certain of these difficulties were recognized by P. J.Crosland-Taylor who proposed, in an article entitled A Device forCounting Small Particles Suspended in a Fluid through a Tube", whichappeared in the Jan. 3, 1953 issue of the publication NATURE, page 37,injecting a suspension of particles to be counted into a stream ofliquid flowing in the same direction. Under conditions in which verylittle turbulence existed, the relatively wide column of particles wasaccelerated by the faster flowing stream to form a narrow columnsurrounded by the sheath liquid previously selected to match the indexof refraction of the suspension.

The sheathed stream was enclosed in a block-like device for observation,and the author made no mention of any light refraction problem existingwith reference to the outer interface of the sheath, probably, becausein that device the viewing parts did not permit close observation of thesample. It presently appears that no thought was then given to theproblem of refraction of light at both interfaces of a cylindricalsheath stream which encloses a cylindrical inner stream.

Subsequently, further experimental work was reported along the samegeneral lines by P. F. Mullaney, M. A. Van Dilla, 1. R. Coulter, and P.N. Dean, in an article entitled "Cell Sizing: A Light-ScatteringPhotometer for Rapid Volume Determination which appeared in thepublication THE REVIEW OF SCIENTIFIC INSTRUMENTS, Vol. 48, No. 8, Aug.1969. A flow chamber was described in which the sheathed stream wasinjected into an ambient body of liquid confined by the chamber in thewindowed observation area upstream of a restrictive orifice and carriedtherebeyond through the orifice. This work was based on the earlier workof P. J. Crosland-Taylor.

The later use by others of the last-mentioned flow chamber was fraughtwith optical problems among which was the preclusion of optics withclose working distances, say, in the order of 2 mm, and multipledifficulties, same caused by entrapment of air bubbles, involvingundesirable refraction of light in the observation area including butnot limited to refraction of light at the interfaces of the sheathstream. Also, observation was restricted to a small area, upstream ofthe aforementioned restrictive orifice.

The present invention effectively tends to obviate the aforementioneddifficulties, particularly in dark field light-scattering photometrictechniques.

SUMMARY OF THE INVENTION It is an object of the invention to provide animproved method and apparatus for optical analysis by photometry of asubstance flowing in a liquid stream within a coaxial sheath stream of atransparent liquid which sheath stream flows in the same direction andentrains the inner stream so as to confine it in concentricrelationship.

Another object includes the narrowing of the sheathed stream to a verysmall diameter in which it may be confined by a wall structure in thearea of examination, and the avoidance in this area of any more volumeof the sheathed stream than necessary to carry the sample. This tendseffectively to reduce any ambient fluid which might obscure the sample.

A further object is to provide equal and opposite refraction of light inphotometric analysis of a cylindrical sheathed stream by varying theradius of the inner stream within limited but practical ranges throughthe control of the relative flow of the inner and outer streams.

According to the invention, there may be provided in such apparatus aflow chamber having an elongated passageway portion provided with anoutlet end and at the other end a tube inlet of substantially smallerdiameter extending concentrically a distance into the passageway portionand terminating forwardly in a free tube end. The'flow chamber furthercomprises a second inlet in the passageway portion at a location adistance rearwardly from the free tube end. The flow cell furthercomprises a restriction in the aforementioned passageway portionintermediate the aforementioned outlet end thereof and the free tubeend, which defines a round opening, the internal surfaces of thepassageway portion of the tube being circular.

Provision is made for flowing a sample stream through the tube inletinto the passageway portion and for flowing a sheath stream into theaforementioned second passageway inlet at a greater velocity than thesample to entrain the latter so as to increase the velocity of thesample stream and narrow it as the streams flow toward theaforementioned restriction of the passageway portion wherein they arenarrowed proportionately, thereby both being accelerated.

A photometer is provided downstream from the upstream extremity of therestriction of the passageway portion and includes a light source, onone side of the sheathed stream in a position to direct light'onto thesample stream, and a light detector externally of the sheathed stream inan angular position to detect the photometric results of impingement oflight on the contents of the sample stream. A further provision is madefor controlling the relative flow of the streams which controls theradius of the sample stream, so that the last named radius may be variedand thereby compensate for refraction of light at the interfaces of thesheath stream.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 is a diagramatic view of apparatus for optical analysis byphotometry including a flow chamber, embodying the invention;

FIG. 2A is a view of the flow chamber of FIG. 1 illustrating it inlongitudinal horizontal section;

FIG. 2B is a longitudinal elevational sectional view of the flowchamber;

FIG. 3 is an enlarged sectional view taken on line 3-3 of FIG. 2B,illustrating the sheathed stream within the flow chamber;

FIG. 4 is a further enlarged, fragmentary view in section taken on line4--4 of FIG. 2B, illustrating the sheathed stream within the flowchamber and indicating how refraction of light at the interfaces of thesheath stream is compensated; and

FIG. 5 is a view similar to FIG. 2A illustrating in vertical section amodified form of the flow chamber.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 there is shown theprincipal elements of apparatus for optical analysis by photometry of asubstance flowing in a liquid stream within a coaxial sheath stream of atransparent liquid, the illustration being by way of example only. Thereis indicated at 10 a supply of transparent liquid for the sheath stream,the source being illustrated as a flask from which passes tube 11emptying into an elevated vessel 12 for the sheath stream. The vessel 12has an overflow outlet including a tube 13 to carry off excess liquidand return it to the source 10 by gravity.

A pump 14 is provided to convey liquid from the source 10 to the vessel12 which forms a constant-level reservoir for the sheath stream liquid.The bottom of the vessel is provided with a liquid outlet connected to agravity feed tube 15 connecting the vessel 12 with a lower flow chamberindicated generally at 16. The flowcharnber is gen'erally'of elongatedtubular shape and, in the illustrated form, the tube 15 is branched sothat the flowchamber hasa pair of liquid inlets 17 for the sheath streamwhich are arranged opposite one another in the side-.

rninating forwardly .a distance within the longitudinal passageway ofthe chamber 16 in a free end. The tube 18 is ar- 3, 1 960 withoutcausing undue pulsationsofthe sample within ranged concentrically 'withreference to the longitudinal passageway of theflow chamber, the tube 18being of substantially smaller outer diameter than the which it extends.v v v The other'end of the flow chamber 16 is a discharge end passagewayportion into connected to a tube 19 discharging into a suitablereceptacle which-is here shown as a stoppered flask 20. Vacuum tube 21is connect'ed. to the upper portion of the flask 20 to create avacuumfor the purpose of withdrawing the sheathedstream from the flowchamber 16, andto this end the tube 21 is con- ;nected to. a vacuum pump22 through a regulator 23, and the tube 21' isprovided with a suitablepressure guage24. v

The flow chamber 16, details of which will be discussed hereinafter withreference to other views of the drawings, is structured largely of atransparent material such as a suitable glass, and has associated with atransparent region thereof a photometer including a light source 25 atone sideof the flow chamber and at the opposite'sidea'light detector 26so that light from the sourcepasses through the-contents'of the flowchamber to the light detector in the illustrated form.

This arrangement, however,'is not a limitation. In this connection itmay be noted that while the light source and light detector areindicated to be in opposing relationship, the light detector might bearranged at right angles to the path of light impinged on the sheathedstream todetect fluoresence, for example, in the contents of the flowchamber 16. In a certain photometric technique, the light emitted fromthe light source andimpinged on the stream to be analyzed may bereflected backin the direction of the light source for a distance beforebeing diverted vto the light detector convenientlylocated to receivesuch diverted light rays, and such a technique is also possibleaccording to the invention. The illustrated arrange 'ment of the lightsource and light detector permits analysis of a sample by its lighttransmitting characteristics or its light absorbing characteristics,

techniques. Y I v For illustrative purposes it may be considered thatthe sample contains particles in suspension to be counted by a forwardscattering of lightby the particles, that is, toward the light detectorin the position shown, as they pass substantially one Thesample streammay be fed to the inlet tube 18 intermittently or continuously and bepulled or pushed for introduc-- tion into the flow chamber. U.S. Pat.No. 2,879,14l issued and; also by. light-scattering desired the sheath;stream, like thesample stream, may be pushed or, pulled by a pump forintroduction into the flow inlet forthe sheath streamf, V. v 7

:It will be apparent that theflow chambermay haveasingle inlet for thesheath stream, such as one concentric with .the tube 18. lt is.necessary, here, that the sheath streamhave a sufficient distance oftravel fromjts point of entry to the free forward end of 'the sampletube l 8-'to completely fill the passageway portion and establishsteadystate laminar flow surrounding the tube in order to properly entrain thesample stream injectedthereinto from .the'tube 18 on its passage towardthe discharge end of the flow-chamber connected to chamber inlets 17,which may be considered together as an the tube 19, as will more readilyapparent fromthe discussion hereinafter of other views of the drawings.1

As will appear more fully hereinafter, the entrained sample stream isreduced in diameter after leaving the tube 18, and the radius of thesample stream may be variedby-controlling the relative flow of thesample and sheath streams as previ ously indicated. As it is usuallydeemed undesirable to place a restrictive device'such as a valve or thelike in the sample stream inlet line due to the riskof clogging. ofthesample stream, a needle valve 28 maybe interposedin the sheath streamtube 15 intermediate the vessell2 and the chamber inlet 17 tocontrol theinlet flowof the sheath stream'to the flow chamben-Aresistor may be usedin place of the valve 28, ifv desired. It will .be evident thatif theflow of the sheath stream is reduced, theradius of the sample stream isenlarged. Also, if the sheath-stream flow is' increased, the radius ofthe sample stream. diminishes. Refraction of light impinged on thesample stream by thelight source 25 is a" function, atleastin part, ofthe radius of the sample stream. v

Referring now to'the details of theflow chamber 16 shown in FIGS. 2Athough 4, the chamber includes an elongated tubular body 30 oftransparent glass material having diametrically opposite .side' arms inalignment with one another providing the inlets 17 for thesheath'stream, in which arms nipple fittings may be received,respectively, for connection to the flow chamber and are ofapproximately the: same internal after another in a stream intermediatethe light source and the Mar. 24, 1959 discloses-(the disclosure'ofwhich is incor-U porated herein by reference) a suitable automatedsample supply apparatus, not shown, which has provision for holding aplurality of samples, which may be used. The samples of a se- I ties intubing may be separated from one another by a seg:

menting fluid which maintains the integrity of the samples and tends tocleanse the tubing wall as the sample stream passes toward theexamination area as described in the last-mentioned patent. Usually anysegmenting fluid is removed prior to entry of a smple into the flowchamber as by a device, not

shown, such as that illustrated and described in US. Pat.,No.

3,109,714 issued Nov. 5, 1963.1t has been found that samples.

may be conveniently transmitted to and through the last.-' named deviceby a peristaltic pump, not shown, such as that illustrated and describedin 0.8. Pat. No. 2,935,028 issued May diameter as the longitudinalportion 32 of the flow chamber passageway with which theycommunicate,-which maybe approximately .125 inch.

. The longitudinal passageway portion 32 continues tothe rear end of theflow chamber and is closed by a plug 34 through the center of which,extends'the mid-portion of the sample stream inlet tube 18, so that thetube Isis concentrically supported in fluid-tight relation thereby inthepassageway portion 32. The forward free end 36 of the tube 18 extendsbeyond the inlet arms 17 and terminates in the passagewayportion 32whichis circular in cross section. The cylindricaltube 18 which has anouter diameter substantially smaller than that Of the passageway portion32 may have an inner diameter of approximately 0.0195 inch and be con- 7stituted by hypodermic tubing or of a small-diameter tube structure of anon-corrosive metal. lts'fluid passageway is circular in cross section.

As shown in nos. 24 and 2B, therear end portion of thetube 18 isreceived in one end-of a sleeve '37 the other end of which sleevemayreceive a nipple fitting 38 for connection to v a suitable sampletube not shown. A distance forwardly of the free end 36 of the tube 18,the inner wall surface of the longitudinal passageway in the tubularbody 30 slopingly narrows creating a restriction, indicated at 42, ofcircular cross section defining an orifice and extending forwardly inthe area of and beyond the light path between the light source 25 andthe light detector 26 as shown in FIGS. 2A and 2B.

In the region of the light path, outer wall surfaces of the tubular bodyare thinned and flattened, as at 44, on opposite sides thereof inopposing relation to the light source and the light detector to minimizelight refraction at the outer surface of the tubular body 30 and topermit the aforementioned optical elements 25, 26 to closely approachthe fluid contents of the restricted passageway portion 42, as indicatedin FIGS. 2A and 3. This close working distance of the optical elementsfrom the fluids contents may be approximately 0.010 inch, and permitsuse of a high numerical aperature condenser and objective. If desired,the portion of the tubular body 30 of the flow chamber in the light pathmay be immersed in optical oil for a refractive index match.

The restriction 42 in the tubular body 30, which may be 0.010 inch, isillustrated as extending through the thickened discharge end 40 (FIG.2A) of the body 30 received in one end of a sleeve 41 the other end ofwhich receives a nipple fitting 43 for connection to the discharge tube19 (FIG. 1) for discharge of the composite liquid stream from the flowchamber into the waste receptacle or trap 20 shown in FIG. 1. Theillustrated vacuum pump 22 connected through tube 21 to the receptacle20 effectively discharges the flow chamber, and it has been found thatthe pump 22 may be run at varying vacuums without changing the radialdimension of the sample stream within the sheath stream in theexamination area provided by the restricted passageway portion 42 of theflow chamber. 4

It will be understood from the foregoing that when the sample stream isinjected through the tube 18 into the passageway portion 32 of the flowchamber it is entrained and accelerated by the faster flowing laminarsheath stream, and the streams are proportionately narrowed andaccelerated as they are influenced by the restriction 42 of thepassageway prior to reaching the examination area. Hence, smallparticles in diluted suspension forming the sample stream tend to followone another through the passageway portion 42 rather than pass abreastof one another, which enables the particles to be counted by the actionof the photometer which operates a suitable recorder not shown. In FIGS.3 and 4 the sample stream is indicated at 46 and the sheath stream at48.

The diameter of the sample stream may be, in a particular instance,depending on the relative flow of the sample and sheath streams,approximately 0.003 inch. Also, by way of example, the sample stream mayequal 9 per cent of the total flow. In such circumstances a total flowof the combined streams through the flow chamber of 5 ml per minute, or3 millionths of a cubic foot per second, equal a Reynolds number of5 10.

In the modified form of the invention illustrated in FIG. 5, the flowchamber, indicated generally at 50, has an elongated block-like body 51vertically arranged provided through its upper end with a pair ofconverging bores or sheath stream inlets 52 respectively receivingnipple fittings 54 for connection to the respective branches of a sheathstream supply tube similar to the tube previously described withreference to FIG. 1. These inlets 52 converge, as shown, in a central,longitudinal bore or passageway portion 56 of the body 51, extendingthrough the lower end thereof. Through the upper end portion of the body51, there is provided a central longitudinal bore intermediate thesheath stream inlets 52 which bore, communicating with the passagewayportion 56, receives a sample stream inlet tube 58, similar to thesample stream inlet tube 18, previously described. The tube 58 extendsthrough a supporting plug 60, provided in an enlargement of thelastmentioned bore, and the tube 58 is concentrically arranged in thepassageway portion 56, with its lower free end 62 terminating a distanceupwardly from the lower end of the passageway portion 56, as illustratedin F IG. 5.

As shown in the last-mentioned view, a restriction is formed in thelower discharge end of the passageway portion 56, the restriction inthis instance being formed by a plug 64 inserted for support in thelower end of the passageway portion 56, the plug 64 having a centralopening 66 defined by a funnel-like surface. From the opening 66 in theplug 64, the sheathed stream is injected downwardly into the ambientatmosphere for examination by a photometer, illustrated as comprising alight source 68, closely located at one side of the stream, and thelight detector 70, located closely to the stream on the diametricallyopposite side thereof, for a light path therebetween. Also, as shown inFIG. 5, there may be provided a funnel 72 to catch the streams shortlyafter they cross the last mentioned light path and collect them fordrainage into a suitable receptacle therebelow, not shown.

In the operation of the flow chamber 50, the sheath liquid supplied tothe inlets 52 of the flow chamber 50 picks up, in the passageway portion56, the sample stream injected into the passageway portion 56 throughthe tube 58, in a manner to entrain it and accelerate the sample stream,narrowing it as the streams flow toward the restriction formed in thepassageway portion 56 by the plug 64, wherein they are narrowedproportionately, thereby both being accelerated, all in a manner similarto the operation of the flow chamber 16 previously described. Aspreviously indicated, the sheathed stream is unconfined after it exitsfrom the flow chamber 50 through the plug 64 and passes across the lightpath between the light source 68 and the light detector 70. This makespossible extremely short working distances from the sheathed stream tothe optical elements 68, 70, with attendant apparent advantages.

To compensate for the refraction of light at the interfaces of thesheath stream in the area in which the stream is examined, the radius ofthe inner or sample stream may be varied, as in the use of thepreviously described flow chamber 16, by adjusting the relative flow ofthe sheath and sample streams. This control of the relative flow of thestreams may be accomplished in the previously described manner. Anotheradvantage of the form of the invention shown in FIG. 5 over that shownin FIG. 1, is that by injecting the sheathed stream into the ambientatmosphere for examination, a significant pressure drop may be avoidedin the area of examination.

However, one of the advantages of the form of the invention shown inFIG. 1, is that the flow chamber 16 may be oriented in any position sothat the optical elements associated with the flow chamber mayaccordingly be positioned, that is, vertically or horizontally. Iftheflow chamber 16 is arranged vertically with the flow directed upward, itis obvious that any air bubbles which might be caught in the chamberwill be swept to the upper end thereof and out of the viewing area.Still another advantage of the form of FIG. 1, is that the sheathedstream is confined in the examination area so as to prevent splatteringof the optical elements associated with the flow chamber as by anaberration in the sheathed stream.

Referring now to the optical problems, specifically refraction of light,overcome by the invention, it is known that the external surface of acylinder such as the sheath stream will refract light if the substancewith which it is in contact has a different index of refraction, such asair or glass. This refraction may be compensated within workable limitsincluding the indexes of refraction of the outer substance such as airor glass, the sheath stream and the sample stream.

Compensation is achieved if rays 74 (FIG. 4) parallel to the opticalaxis 75 reach the center line of the sample stream in parallel relationto the axis 75 of light from the aforementioned light source 25. Thiscompensation may be obtained by determining and establishing the correctradius of the sample stream with reference to the particular operatingconditions prevailing at the time including the last-mentioned indexesof refraction. The radial dimension of the sample stream must be such asto bring about equal and opposite refraction at the two interfaces ofthe sheath stream.

In the form illustrated in FIG. 4 in which the sheathed stream isenclosed within a hollow cylindrical wall surface, the index ofrefraction N, of the sample stream must be greater than the index ofrefraction N, of the sheath stream to obtain compensation of refractionat the interfaces of the sheath stream. The converse is true in thesituation of FIG. 5 in which the sheath stream in the area ofexamination is unconfined,

streamsis less than the absolute difference in refraction indexes of theouter stream and that (here, glass) to which it is externally exposed.

Thus,,in the following an example, where N is 1.51; N, is l .36; N isapproximately 1.38; and r,, the radius of the sheath stream, is 0.005inch: in solving for r, the radius of the sample stream, the followingequation is used:

1 r=a p proximately .00076 inch from elementary optics wherein:

' In the foregoing example, the sample stream is constituted by human.blood diluted with propylene glycol and in which the red cells arehemolyzed. The red cell ghosts have the same index of refraction as thediluent so that the-red cells are rendered invisible, for the countingby photometric means, as aforesaid, of the white cells. One obviousadvantage of the invention is that there is no requirement in the use ofthe flow chamber that the index of refraction of the sheath stream matchthe index of refraction of the sample stream.

The photometer has a conventional ocular, not shown, to observe, withthe human eye, the flow of the stream in the flow chamber so that it maybe determined whether or not refractive errors have been compensated. inthis connection a conventional target, not shown, of the opticalelements, projected through the flow chamber is brought into sharp focusat the particular sample stream radius which achieves compensation oflight refraction as indicated above. The photometric viewing area shouldbe larger than the diameter of the sample team.

It is believed the many advantages of this invention will now beapparent to those skilled in the art. Theforegoing description isillustrative, rather than limiting, as a number of variations andmodifications may be made without departing from the true spirit andscope of the invention. The invention is limited only to the scope ofthe following claims.

What is claimed is:

1. Apparatus for optical analysis of a sample stream including a liquidin a coaxial sheath stream liquid comprising: means defining a flowchamber. having an elongated passageway portion having a forward outletend and at a rear end of said portion a tube inlet of substantiallysmaller diame ter than said passageway portion extending concentricallya distance forwardly into said passageway portion and terminatingforwardly in a free tube end, the last-named means defining a secondinlet in said-passageway portion at a location a distance rearwardlyfrom said free tube end, and the lastnamed means also defining arestriction with a narrow sloping approach in said passageway portionintermediate said outlet end thereof and said free tube end, theinternal andexternal surfaces of said free tube end and the internalsurface of said passageway portion being circular in cross section,means for flowing a sample stream through said'tube inlet into saidpassageway portion, means for flowing a sheath stream into said secondpassageway inlet at a greater flow rate than the sample stream toentrain the latter so" as to increase the velocity of the sample streamand narrow it as the streams flow toward said restriction of thepassageway portion, photometric means downstream from the upstreamextremity of restriction of the passageway portion in proximity to thesheathed stream and including a light source on one side of the sheathedstream in a position to direct lightonto the contents of the samplestream anda light detector externally of the sheathed stream in angularposition to detect the photometric results of impingement of light onthe sample stream, and means controlling therelative flow rates of saidstreams into said flow chamber, which controls the radius of the sampleI stream, so that in the area where said light is directed on the samplestream the last-named radius may be varied proportionately to the radiusof the inner surface of the sheath stream for equal and oppositerefraction of light at the interfaces of said sheath stream. v

2. Apparatus as defined in claim 1, wherein: said means controlling therelative flow rates of said streams comprises a device operative torestrict the flow of the sheath stream into the flow chamber.

3. Apparatus as defined in claim 1, wherein: said means for flowing thesheath stream into said flow chamber comprises a constant-levelreservoir establishing a head of sheath stream liquid.

4. Apparatus as defined in claim 1, wherein: said means for flowing thesample stream into said tube inlet of the flow chamber comprises a pumpupstream of the tube inlet.

5. Apparatus as defined in claim 1, wherein: said outlet end of the flowchamber is connected to a pump.

GsApparatus asdefined in claim 1, wherein: said means controlling therelative flow rates of the streams comprises a valve operative to varythe flow of the sheath stream into the flow chamber. v

7 Apparatus as defined in claim 1, wherein: said means for flowing thesample stream into said sample tube inlet of the flow chamber comprisesa pump upstream of the tube inlet, said outlet end of the flowchamberbeing connected to a liquid trap throughan outlet conduit, andfurther comprising a vacuum pump 'operatively connected to thelast-named outlet conduit.

V 8. Apparatus as defined in claim 1, wherein: the flow chamber isvertically arranged.

9. Apparatus as-defined in claim 1, wherein: the sheathed stream isdirected from said outlet end of the flow chamber into a gas, and saidphotometric means examines the sheathed sample stream in said gas.

10. Apparatus as defined in claim Lwherein: the sheathed stream isdirected into ambient air from said outlet end of the flow chamber, andsaid photometric means examines the sheathed sample stream in saidambient air.

11. Apparatus as defined inv claim 1, wherein: the flow chamber ishorizontally arranged.

12. Apparatus as defined in claim 1, wherein: said means defining a flowchamber comprises a tubular body having said restriction of thepassageway portion therein.

13. Apparatus as defined in claim .1, whereimsaid means defining a flowchamber comprises a tubular body having said restriction of thepassageway portion therein, said restriction enclosing the sheathedstream where light from said source. is impinged on the sample stream.

14. A method for optical analysis of a sample stream including a liquidin a coaxial sheath stream liquid comprising: providing means definingan elongated passageway portion of circular cross section in a flowchamber which portion has at one end thereof a circular restriction;flowing a first laminar liquid stream into said passageway portion in adirection toward said restriction; concurrently flowing in the samedirection a slower moving liquid stream of cylindrical cross section andof a substantially smaller diameter than said first stream, containing asample, into the first stream concentrically so that the latter sheathsand entrains the second stream, accelerating and narrowing it as thestreams approach said restriction in a concentric relation to oneanother; directing an impinging light beam of a photometer, in adirection transversely of the aforementioned direction of flow, onto thesamplecontaining stream for photometric analysis of the sample by alight detector of the photometer, downstream from the upstream extremityof said restriction; and controlling the relative flow rates of thestreams into said passageway portion, which controls the radius of thesecond or sample stream, so that in the area where said light beamimpinges said sample stream the last-named radius may be variedproportionately to the radius of the inner surface of the sheath streamfor equal and opposite refraction of light at the interfaces of thesheath stream.

15. The method as defined in claim 14, wherein: the step of controllingthe relative flow of the streams into said flow chamber comprisescontrolling said sheath stream.

16. The method as defined in claim 14, wherein: the step of flowing thesheath stream into the flow chamber comprises flowing the sheath streamfrom a constant-pressure source.

17. The method as defined in claim 14, further comprising introducingthe sheath and sample streams into the How chamber under positivepressure, and withstanding the sheath stream from the flow chamber undernegative pressure through an outlet of the flow chamber downstream fromsaid restriction.

18. The method as defined in claim 14, further comprising narrowlyconfining the sheath stream where said light beam is impinged on thesample stream.

19. The method as defined in claim 14, further comprising directing thesheathed stream into a gas from the flow chamber in a downward directionand examining the sheathed stream by the photometer in said gas.

" i t 8 t I UNITED STATES PATENT OFFICE CERTIFICATE :OF CORREC' IICPNPatent No. 3 1,460 Dated May 9, 1972 Inventor(s) Alan H- -kind Qt a1 Itis certified that error appears in the above-identified patent andlthatsaid Letters Patent I are hereby corrected as shown below:

0n the cover Sheet [72] the inventor's name "Alan H. 'E lking" shouldread Alan H. Elkind Signed and sealed this 7th day of Novembervl972';

(SEAL) Attest:

EDWARD M.FLEI'CHER,JR. ROBERT GOTTSCHAIK Attesting Officer Commissionerof Patents )RM p' v USCOMM-DC 6O376-P69 ll 5. GOVERNMENT PRINTINGOFFICE; I96? 0-386-33

1. Apparatus for optical analysis of a sample stream including a liquidin a coaxial sheath stream liquid comprising: means defining a flowchamber having an elongated passageway portion having a forward outletend and at a rear end of said portion a tube inlet of substantiallysmaller diameter than said passageway portion extending concentrically adistance forwardly into said passageway portion and terminatingforwardly in a free tube end, the last-named means defining a secondinlet in said passageway portion at a location a distance rearwardlyfrom said free tube end, and the last-named means also defining arestriction with a narrow sloping approach in said passageway portionintermediate said outlet end thereof and said free tube end, theinternal and external surfaces of said free tube end and the internalsurface of said passageway portion being circular in cross section,means for flowing a sample stream through said tube inlet into saidpassageway portion, means for flowing a sheath stream into said secondpassageway inlet at a greater flow rate than the sample stream toentrain the latter so as to increase the velocity of the sample streamand narrow it as the streams flow toward said restriction of thepassageway portion, photometric means downstream from the upstreamextremity of said restriction of the passageway portion in proximity tothe sheathed stream and including a light source on one side of thesheathed stream in a position to direct light onto the contents of thesample stream and a light detector externally of the sheathed stream inangular position to detect the photometric results of impingement oflight on the sample stream, and means controlling the relative flowrates of said streams into said flow chamber, which controls the radiusof the sample stream, so that in the area where said light is directedon the sample stream the last-named radius may be varied proportionatelyto the radius of the inner surface of the sheath stream for equal andopposite refraction of light at the interfaces of said sheath stream. 2.Apparatus as defined in claim 1, wherein: said means controlling therelative flow rates of Said streams comprises a device operative torestrict the flow of the sheath stream into the flow chamber. 3.Apparatus as defined in claim 1, wherein: said means for flowing thesheath stream into said flow chamber comprises a constant-levelreservoir establishing a head of sheath stream liquid.
 4. Apparatus asdefined in claim 1, wherein: said means for flowing the sample streaminto said tube inlet of the flow chamber comprises a pump upstream ofthe tube inlet.
 5. Apparatus as defined in claim 1, wherein: said outletend of the flow chamber is connected to a pump.
 6. Apparatus as definedin claim 1, wherein: said means controlling the relative flow rates ofthe streams comprises a valve operative to vary the flow of the sheathstream into the flow chamber.
 7. Apparatus as defined in claim 1,wherein: said means for flowing the sample stream into said sample tubeinlet of the flow chamber comprises a pump upstream of the tube inlet,said outlet end of the flow chamber being connected to a liquid trapthrough an outlet conduit, and further comprising a vacuum pumpoperatively connected to the last-named outlet conduit.
 8. Apparatus asdefined in claim 1, wherein: the flow chamber is vertically arranged. 9.Apparatus as defined in claim 1, wherein: the sheathed stream isdirected from said outlet end of the flow chamber into a gas, and saidphotometric means examines the sheathed sample stream in said gas. 10.Apparatus as defined in claim 1, wherein: the sheathed stream isdirected into ambient air from said outlet end of the flow chamber, andsaid photometric means examines the sheathed sample stream in saidambient air.
 11. Apparatus as defined in claim 1, wherein: the flowchamber is horizontally arranged.
 12. Apparatus as defined in claim 1,wherein: said means defining a flow chamber comprises a tubular bodyhaving said restriction of the passageway portion therein.
 13. Apparatusas defined in claim 1, wherein: said means defining a flow chambercomprises a tubular body having said restriction of the passagewayportion therein, said restriction enclosing the sheathed stream wherelight from said source is impinged on the sample stream.
 14. A methodfor optical analysis of a sample stream including a liquid in a coaxialsheath stream liquid comprising: providing means defining an elongatedpassageway portion of circular cross section in a flow chamber whichportion has at one end thereof a circular restriction; flowing a firstlaminar liquid stream into said passageway portion in a direction towardsaid restriction; concurrently flowing in the same direction a slowermoving liquid stream of cylindrical cross section and of a substantiallysmaller diameter than said first stream, containing a sample, into thefirst stream concentrically so that the latter sheaths and entrains thesecond stream, accelerating and narrowing it as the streams approachsaid restriction in a concentric relation to one another; directing animpinging light beam of a photometer, in a direction transversely of theaforementioned direction of flow, onto the sample-containing stream forphotometric analysis of the sample by a light detector of thephotometer, downstream from the upstream extremity of said restriction;and controlling the relative flow rates of the streams into saidpassageway portion, which controls the radius of the second or samplestream, so that in the area where said light beam impinges said samplestream the last-named radius may be varied proportionately to the radiusof the inner surface of the sheath stream for equal and oppositerefraction of light at the interfaces of the sheath stream.
 15. Themethod as defined in claim 14, wherein: the step of controlling therelative flow of the streams into said flow chamber comprisescontrolling said sheath stream.
 16. The method as defined in claim 14,wherein: the step of flowing the sheath stream into the flow chambercomprises flowing the sheath stream from a constant-pressure soUrce. 17.The method as defined in claim 14, further comprising introducing thesheath and sample streams into the flow chamber under positive pressure,and withstanding the sheath stream from the flow chamber under negativepressure through an outlet of the flow chamber downstream from saidrestriction.
 18. The method as defined in claim 14, further comprisingnarrowly confining the sheath stream where said light beam is impingedon the sample stream.
 19. The method as defined in claim 14, furthercomprising directing the sheathed stream into a gas from the flowchamber in a downward direction and examining the sheathed stream by thephotometer in said gas.